1. Field of the Invention
The present invention relates to an optical deflection apparatus that changes a direction of a reflected light with respect to an incident light, the technique being applicable to an electrophotographic imaging apparatus such as a printer or a copier, and an image/video projection display apparatus such as a projector or a digital theater system.
2. Description of the Related Art
In the prior art, an optical switch device using electrostatic power is disclosed by K. E. Petersen, the disclosure relating to a device that switches a reflection direction of light by causing a cantilever beam to bend using electrostatic power, and an optical deflection system implementing such a device (see Applied Physics Letters, Vol. 31, No. 8, 1977, pp. 521˜523; Japanese Patent No. 2941952; Japanese Patent No. 3016871). Also, D. M. Bloom et al. discloses a device that realizes optical switching by driving a grating by electrostatic power (see Optics Letters, Vol. 7, No. 9, pp. 688˜690).
In Japanese Patent Laid-Open Publication No. 6-138403, an imaging apparatus applying an optical deflection system is disclosed, the apparatus implementing digital micro-mirror devices (DMD) in one dimensional or two dimensional arrangements.
L. J. Hornbeck discloses a torsion beam type digital micro-mirror device and a cantilever beam type digital micro-mirror device as configurations of the digital micro-mirror device (see Proc. SPIE Vol. 1150, pp. 86˜102, 1989). It is noted that in the torsion beam type digital micro-mirror device and the cantilever beam type digital micro-mirror device disclosed by L. J. Hornbeck, a tilted mirror unit is used, and the mirror unit used in this prior art example has at least one fixed end.
In Japanese Patent Laid-Open Publication No. 2000-2842, a device that realizes high speed optical deflection by deforming a dual-side fixed beam to bend into a cylindrical shape is disclosed.
An exemplary application of the optical switch device in a commodity product presently being manufactured is disclosed by L. J. Hornbeck in “A MEM-Based Projection Display”, PROCEEDINGS OF THE IEEE, Vol. 86, No. 8, August 1998, pp 1687˜1704. The disclosure pertains to a projection type image display apparatus in which plural torsion beam type optical switch devices are implemented in a two-dimensional arrangement, and an optical signal corresponding to image information of each pixel is guided to a projection lens to display an image. In this prior art example, one light source is used, and light generated at this light source passes through a rotating color wheel to be successively converted into R, G, B color light, after which the light is incident to a chip (optical switch devices arranged into an array) and reflected so that an optical signal corresponding to image information in RGB colors is successively guided to the projection lens to display an image. By using the above system, an image may be displayed using one light source and one chip, and a relatively low-priced projection type image display apparatus may be realized.
Also, another system for displaying an image in a projection type image display apparatus implementing the above described optical switch device is disclosed by L. J. Hornbeck et al. in “Using ZEMAX Image Analysis and User-Defined Surfaces for Projection Lens Design and Evaluation for Digital Light Processing TM Projection Systems”, Optical Engineering, Vol. 39, No. 7, July 2000, pp. 1802˜1807. In this prior art example, one light source is used, and light generated from this light source is passed through a TIR (Total Internal Reflection) PRISM, after which the light is passed through a COLOR PRISM that realizes color separation and color synthesis. Consequently, the light is separated into three color lights, which are incident to three chips. Then, the lights may be reflected in a desired direction, and may be passed through the COLOR PRISM once more for color synthesis. Then, the synthesized light as an optical signal may be guided to the projection lens to display an image. Although the projection type image display apparatus using this system is not inexpensive, R, G, B color signals may be simultaneously displayed, and thereby, the display time of each color in one frame may be maximized, and a high luminance projection type image display apparatus may be realized. It is noted that the above systems of the projection type image display apparatuses are also described in “Digital Micro-Mirror Device”, Ohyo Butsuri, Vol. 68, No. 3, 1999, pp. 285˜289.
In Japanese Patent Laid-Open Publication No. 2002-131838, a projection type image display apparatus implementing the optical switch disclosed by D. M. Bloom that drives a grating by electrostatic power is disclosed. A projection type image display apparatus according to this prior art example includes a laser light source and a space modulator that implements the optical switches in a one-dimensional arrangement, and is adapted to project an image on a screen by scanning, with a scan mirror, a light flux including color synthesized image components of one vertical or horizontal line. This projection type image display apparatus has to use a laser light source to realize the functions of the optical switch, and this inevitably raises the price of the apparatus.
In the cantilever type optical switch or digital micro-mirror device, it is difficult to secure stability of the beam, and the response speed is slow. In the torsion beam type digital micro-mirror device, the mechanical strength of a hinge portion (torsion beam) may be degraded upon long term use. In the optical switch device disclosed in Japanese Patent No. 2941952 and Japanese Patent No. 3016871, the wavelength of the incident light is restricted. As for the device disclosed in Japanese Laid-Open Patent No. 2000-2842, namely, a device in which a parallel space is provided between electrodes and where a dual side fixed beam is bent into a cylindrical shape by an electrostatic force generated between the electrodes, high speed deformation may be realized so that the response speed may be increased; however, since both sides of the beam are fixed, the drive voltage is high compared to the cantilever beam type or torsion beam type device.
FIGS. 1A and 1B are diagrams showing an exemplary configuration of an optical deflector according to the conventional art. FIG. 1A is a top view of the conventional optical deflector (showing a fulcrum member 103 and electrodes 105a˜105d), and FIG. 1B is a cross-sectional view (cut across line B–B′) of the conventional optical deflector.
In this conventional optical deflector, a member having a light reflection region is displaced by electrostatic attraction, and accordingly, a light flux that is incident to the light reflection region is deflected by changing its reflection direction. The optical deflection apparatus includes a substrate 101, plural regulating members 102, a fulcrum member 103, a sheet member 104, and plural electrodes 105a˜105d. The plural regulating members 102 each have a stopper at their upper portion and are respectively placed at plural edges of the substrate 101. The fulcrum member 13 has a peak portion and is placed on the upper surface of the substrate 101.
The sheet member 104 does not have a fixed end, and includes a light reflection region on its upper surface, and a conductor layer made of an element that is at least partially conductive, the sheet member 104 being movably implemented within a space between the substrate 101, the fulcrum member 103, and the stoppers. The plural electrodes 105a˜105d are implemented on the substrate 101 and are arranged substantially opposite to the conductor layer of the sheet member 104.
The conventional optical deflection apparatus has the following advantages.    (1) Since the tilt angle is determined by the contact between the fulcrum member, the substrate, and the sheet member, the deflection angle of the mirror may be stably and easily controlled.    (2) Since the film sheet member may be easily rotated around the fulcrum member by applying differing electric potentials to opposing electrodes, a high response speed may be obtained.    (3) Since the sheet member does not have fixed ends, it is not deformed into a twisted state, for example, so that long-term degradation may be reduced and the sheet member may be driven with a low voltage.    (4) Since a miniaturized and light-weight sheet member may be formed through a semiconductor process, the shock from collision with the stoppers may be reduced and long-term degradation may be reduced.    (5) By arbitrarily determining the configurations of the regulating members, the sheet member, and the light reflection region, the ON/OFF ratio of the reflection light (e.g., S/N ratio in an imaging apparatus, and contrast ratio in a video apparatus) may be improved.    (6) Since a semiconductor process and device may be used, miniaturization and integration may be realized at low cost.    (7) By implementing plural electrodes and a fulcrum member in the middle, light deflection in one axis and two axis directions are possible.
In the following, a drive method of the conventional optical deflection apparatus is described with reference to FIGS. 2A˜2D and FIG. 3.
FIGS. 2A˜2D illustrate how the sheet member of the optical deflection apparatus of FIG. 1 is driven and tilted. FIG. 2A is a cross-sectional view of the conventional optical deflection apparatus across line A–A′ during OFF operation time. FIG. 2B is a cross-sectional view of the conventional optical deflection apparatus across line C–C′ during OFF operation time. FIG. 2C is a cross-sectional view of the conventional optical deflection apparatus across line A–A′ during ON operation time. FIG. 2D is a cross-sectional view of the conventional optical deflection apparatus across line C–C′ during ON operation time.
In this example, optical deflection operation is conducted by switching the electric potential being applied to the electrodes 105a˜105d. In FIGS. 2A and 2D, the electrostatic attraction forces generated by the electric potentials applied to the electrodes 105a˜105d are represented by outline arrows.
FIG. 3 is a time chart showing the electric potentials being applied to the respective electrodes of the conventional optical deflection apparatus.
Referring to FIGS. 2A˜2D and FIG. 3, the drive method of the conventional optical deflection apparatus and the tilting operation of the sheet member 104 (i.e., light deflection operation) are described below.
First, in an OFF operation, as is shown in FIG. 3, a high electric potential A is applied to electrode 105a, a low electric potential C is applied to electrode 105b, and an intermediate electric potential B is applied to electrode 105c and electrode 105d. In this way, the sheet member 104 that includes a conductor layer and is arranged to electrically float opposite to the electrodes 105 may have an electric potential equivalent to the intermediate electric potential B between the high electric potential A and the low electric potential C as can be easily reasoned from calculations of a simple closed circuit. Consequently, electrostatic attraction force is not generated at the ON side electrodes 105c and 105d, and the electrostatic attraction force is generated at the OFF side electrodes 105a and 105b, as is shown in FIG. 2A, so that the sheet member 104 tilts toward the OFF side. This operation may be implemented as an OFF operation in a sequence of optical deflection operations as well as a reset operation for initializing the optical deflection operation.
Then, in an ON operation in FIG. 3, the high electric potential A is applied to the electrode 105c, the low electric potential C is applied to the electrode 105d, and the intermediate electric potential B is applied to the electrodes 105a and 105b. In this way, the sheet member 104 that includes a conductor layer and is arranged to electrically float opposite to the electrodes 105 may have an electric potential equivalent to the intermediate electric potential B between the high electric potential A and the low electric potential C as can be easily reasoned from calculations of a simple closed circuit. Consequently, the electrostatic attraction force is not generated at the OFF side electrodes 105a and 105b, and the electrostatic attraction force is generated at the ON side electrodes 105c and 105d as is shown in FIG. 2D so that the sheet member 104 tilts toward the ON side.
In order to improve the integration of the optical deflection apparatus and prevent manufacturing cost increase, the size of the optical deflection apparatus itself is preferably reduced, and a large number of the optical deflection apparatuses are preferably implemented in an application. Thereby, an IC driving the electrode is preferably implemented on the same substrate as that of the optical deflection apparatus. Also, in order to improve the ON/OFF ratio of the reflection light of the optical deflection apparatus, the drive IC is preferably positioned directly below the optical deflection apparatus.
However, the conventional optical deflection apparatus described above includes at least four electrodes, and thereby, it is difficult to arrange ICs driving the four electrodes directly under the optical deflection apparatus when reducing the size of the optical deflection apparatus at the same time.